Compressor crankcase heating control systems and methods

ABSTRACT

A first switching device includes a first and second inputs connected to first and second power lines, respectively, the first and second power lines for receiving a first voltage. The first switching device selectively connects and disconnects the first and second inputs to and from first and second nodes, respectively. A second switching device includes a third input connected to the first node, includes a fourth input connected to a third power line, and includes a first output connected to a first end of a stator winding. A third switching device includes a fifth input connected to the second node and includes a sixth input connected to a fourth power line, the third and fourth power lines for receiving a second voltage that is less than the first voltage. The third switching device further includes a second output connected to a second end of the stator winding. A compressor crankcase heating control module controls the second and third switching devices to control compressor crankcase heating.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/879,875, filed on Sep. 19, 2013. The entire disclosure of theapplication referenced above is incorporated herein by reference.

FIELD

The present disclosure relates to compressors and more particularly tocompressor crankcase heater control systems and methods.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Compressors may be used in a wide variety of industrial and residentialapplications to circulate refrigerant within a refrigeration, heat pump,HVAC, or chiller system (generically “heat pump systems”) to provide adesired heating or cooling effect. In any of the foregoing applications,the compressor should provide consistent and efficient operation toensure that the particular heat pump system functions properly.

Compressors may include crankcases to house moving parts of thecompressor, such as a crankshaft. Crankcases may further includelubricant sumps, such as an oil reservoir. Lubricant sumps includelubricants that lubricate the moving parts of compressors. Lubricationof the moving parts may improve performance and/or prevent damage.

Lubricants in the crankcases may cool to low temperatures when thecompressor is not running. For example, the crankcases may cool due to alow outdoor ambient temperature. Additionally, lubricants may cooland/or be diluted when liquid refrigerant returns to the compressorduring the running cycle. Lubricant cooling may also occur under othercircumstances.

Lubricant properties may change at low temperatures. More specifically,lubricants may become more viscous (i.e., thicker) at low temperatures.Starting a compressor with a low crankcase temperature and/or asignificant amount of liquid within the shell may cause bearing wearand/or decreased performance due to insufficient lubrication.

SUMMARY

In a feature, a compressor crankcase heating control system for a heatpump system is disclosed. A first switching device includes a firstinput connected to a first power line and includes a second inputconnected to a second power line, the first and second power lines forreceiving a first voltage. The first switching device selectivelyconnects and disconnects the first and second inputs to and from firstand second nodes, respectively. A second switching device includes athird input that is connected to the first node, includes a fourth inputthat is connected to a third power line, and includes a first outputthat is connected to a first end of a stator winding of an electricmotor of a compressor. A third switching device includes a fifth inputthat is connected to the second node and includes a sixth input that isconnected to a fourth power line, the third and fourth power lines forreceiving a second voltage that is less than the first voltage. Thethird switching device further includes a second output that isconnected to a second end of the stator winding of the electric motor ofthe compressor. A compressor crankcase heating control module controlsthe second and third switching devices.

In a feature, a compressor crankcase heating control system for a heatpump system is disclosed. A first switching device includes a firstinput connected to a first power line and includes a second inputconnected to a second power line, the first and second power lines forreceiving a first voltage. The first switching device selectivelyconnects and disconnects the first and second inputs to and from firstand second nodes, respectively. A second switching device includes athird input that is connected to the first node, includes a fourth inputthat is connected to a third power line, and includes a first outputthat is connected to: a first end of a first winding of a stator of anelectric motor of a compressor; and a first end of a second winding ofthe stator of the electric motor of the compressor. A third switchingdevice includes a fifth input that is connected to the second node andincludes a sixth input that is connected to a fourth power line, thethird and fourth power lines for receiving a second voltage that is lessthan the first voltage. The third switching device further includes asecond output that is connected to second ends of the first and secondwindings of the stator of the electric motor of the compressor. Acompressor crankcase heating control module controls the second andthird switching devices.

In a feature, a heat pump system is disclosed including: first andsecond heat exchangers; an expansion valve; and a compressor thatincludes an electric motor including a stator, the stator including afirst winding and a second winding. A first switching device includes afirst input connected to a first power line and includes a second inputconnected to a second power line, the first and second power lines forreceiving a first voltage. The first switching device selectivelyconnects and disconnects the first and second inputs to and from firstand second nodes, respectively. A second switching device includes athird input that is connected to the first node, includes a fourth inputthat is connected to a third power line, and includes a first outputthat is connected to at least one of a first end of the first windingand a first end of the second winding. A third switching device includesa fifth input that is connected to the second node and includes a sixthinput that is connected to a fourth power line, the third and fourthpower lines for receiving a second voltage that is less than the firstvoltage. The third switching device further includes a second outputthat is connected to a second end of the first winding and a second endof the second winding. A compressor crankcase heating control moduleincludes a processor and memory, the memory including instructionsexecuted by the processor for, when the first and second inputs aredisconnected from the first and second nodes, respectively: actuatingthe second switching device to connect the fourth input to the firstoutput; and actuating the third switching device to connect the sixthinput to the second output; and, when the first and second inputs areconnected to the first and second nodes, respectively: actuating thesecond switching device to connect the third input to the first output;and actuating the third switching device to connect the fifth input tothe second output.

In a feature, a method includes: selectively actuating a first switchingdevice to connect and disconnect first and second inputs of the firstswitching device to and from first and second nodes, respectively, thefirst input of the first switching device connected to a first powerline, the second input of the first switching device connected to asecond power line, the first and second power lines for receiving afirst voltage; when the first and second inputs are disconnected fromthe first and second nodes, respectively: actuating a second switchingdevice to connect a third input of the second switching device to afirst output of the second switching device, the third input connectedto a third power line, and the first output of the second switchingdevice connected to at least one of a first end of a first winding of astator of an electric motor of a compressor and a first end of a secondwinding of the stator; and actuating a third switching device to connecta fourth input of the third switching device to a second output of thethird switching device, the fourth input connected to a third powerline, the third power line for receiving a second voltage that is lessthan the first voltage, and the second output of the third switchingdevice connected to second ends of the first and second windings; andwhen the first and second inputs are connected to the first and secondnodes, respectively: actuating the second switching device to connect afifth input of the second switching device to the first output of thesecond switching device, the fifth input connected to the first node;and actuating the third switching device to connect a sixth input of thethird switching device to the second output of the third switchingdevice, the sixth input connected to the second node.

In a feature, a method includes: selectively actuating a first switchingdevice to connect and disconnect first and second power lines to andfrom second and third switching devices, respectively, the first andsecond power lines for receiving a first voltage; when the first andsecond power lines are disconnected from the second and third switchingdevices, actuating the second and third switching devices to connectthird and fourth power lines to ends, respectively, of at least onewinding of a stator of an electric motor of a compressor, the third andfourth power lines for receiving a second voltage that is less than thefirst voltage.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1A is a functional block diagram of a first example heat pumpsystem according to the present disclosure;

FIG. 1B is a functional block diagram of a second example heat pumpsystem according to the present disclosure;

FIG. 2 is a perspective view of a compressor with a variable frequencydrive according to the present disclosure;

FIG. 3 is another perspective view of a compressor with a variablefrequency drive according to the present disclosure;

FIG. 4 is a cross-sectional view of an example compressor according tothe present disclosure;

FIG. 5 is a functional block diagram of an example implementation of acrankcase heating control module according to the present disclosure;

FIGS. 6-14 are flowcharts depicting example methods of controllingcrankcase heating according to the present disclosure;

FIGS. 15A, 15B, and 15C are functional block diagrams of examplecrankcase heating control systems of example single phase heat pumpsystems according to the present disclosure;

FIG. 16 is another example implementation of the crankcase heatingcontrol module according to the present disclosure; and

FIGS. 17A, 17B, and 17C are functional block diagrams of examplecrankcase heating control systems of example single phase heat pumpsystems according to the present disclosure.

DETAILED DESCRIPTION

Compressors may include heating elements that heat crankcases in orderto avoid problems related to “cold starting” or “liquid flood-back.”Cold starting may refer to startup of a compressor when lubricantswithin the compressor are cold and diluted by refrigerant. Thelubricants therefore are less viscous and have lower lubricatingcapabilities during cold starting, which may cause higher stress on oneor more compressor components, such as a bearing.

Heating the crankcase of a compressor increases a temperature oflubricants inside the crankcase. Increasing the temperature of thelubricants may improve performance and/or prevent damage to thecompressor due to the increased viscosity of cold lubricants.

Liquid flood-back may refer to when liquid (refrigerant) migrates intothe compressor shell. Liquid migrates back to a compressor when thecompressor is off and the compressor temperature is less than (itssurrounding) ambient temperature. Heating the crankcase of thecompressor may minimize liquid migration to the compressor and mayremove liquid that has migrated to the compressor.

Typical crankcase heating elements, hereinafter referred to as“crankcase heaters,” may operate in different ways. For example, bellyband heaters and positive temperature coefficient (PTC) heaters are twotypes of devices that may be used as crankcase heating elements. Thepresent application involves use of a stator of an electric motor of acompressor to perform crankcase heating.

The stator is a non-moving part of the electric motor in the compressor.When the compressor is on, the stator may magnetically drive a rotorthat in turn drives a crankshaft. The crankshaft may, in turn, drive acompression mechanism of the compressor. When the compressor is in theoff state, the stator may generate heat when supplied with current, andthus the stator may act as a heater for the lubricants inside thecompressor and evaporate liquid refrigerant.

Crankcase heating may be performed continuously while the compressor isin an off state (i.e., not compressing). Continuous crankcase heatingwhile the compressor is in the off state may heat the lubricant morethan is required to avoid cold starting. However, this continuous use ofcrankcase heating is less efficient than desired due to wasted energyfrom excessive heating.

Systems and methods for more efficient crankcase heating are disclosed.Crankcase heating may be turned on or off based on an outdoor ambienttemperature, a compressor temperature, both the outdoor ambienttemperature and the compressor temperature, and/or a current date andtime. For example, crankcase heating may be turned off for apredetermined period (e.g., approximately 3 hours) after the compressoris transitioned to the off state. The predetermined period may be setshorter than a period necessary for a predetermined amount of liquidmigration back to the compressor shell to occur after the compressor istransitioned to the off state. Additionally or alternatively, crankcaseheating may be turned off when the outdoor ambient temperature isgreater than a predetermined temperature (e.g., approximately 75 degreesFahrenheit). Additionally or alternatively, crankcase heating may beturned off when the compressor temperature minus the outdoor ambienttemperature is greater than a first predetermined temperature (e.g.,approximately 20 degrees Fahrenheit), and crankcase heating may beturned on when the compressor temperature minus the outdoor ambienttemperature is less than a second predetermined temperature (e.g., 0degrees Fahrenheit). The first predetermined temperature may be setbased on a temperature indicative of little liquid remaining in thecompressor shell. Additionally or alternatively, crankcase heating maybe turned off when the compressor has been in the off state for apredetermined period (e.g., approximately 3 weeks) and the outdoorambient temperature and the compressor temperature are less than apredetermined temperature (e.g., approximately 55 degrees Fahrenheit).The predetermined period and the predetermined temperature may be setsuch to be indicative of air conditioning being turned off for a season.Additionally or alternatively, crankcase heating may be turned offwithin a predetermined range of dates (e.g., approximately November 1 toapproximately April 1 in the northern hemisphere). Additionally oralternatively, crankcase heating may be turned off for a predeterminedperiod (e.g., approximately 12 am to approximately 10 am daily duringdiurnal cycle). Additionally or alternatively, crankcase heating may beturned off for the next predetermined duration (e.g., the next X numberof days, weeks, or months). Disabling crankcase heating at times whencrankcase heating would otherwise be performed decreases energyconsumption and increases efficiency.

The stator receives a first voltage via power lines to drive the rotor,the crankshaft, and the compression mechanism of the compressor. Thefirst voltage could also be used to perform crankcase heating. However,the first voltage is relatively higher than a voltage needed to performcrankcase heating to sufficiently prevent liquid floodback and coldstarting. The present application therefore discloses systems andmethods for generating and applying a second voltage that is less thanthe first AC voltage for crankcase heating, thereby increasing theefficiency of crankcase heating.

With reference to FIGS. 1A and 1B, functional block diagrams of exampleheat pump systems 5 are presented. The heat pump systems 5 include acompressor 10 that includes a shell that houses a compression mechanism.In an on state, the compression mechanism is driven by an electric motorto compress refrigerant vapor. In an off state, the compressionmechanism does not compress refrigerant vapor.

In the example heat pump systems 5, the compressor 10 is depicted as ascroll compressor and the compression mechanism includes a scroll havinga pair of intermeshing scroll members, as shown in FIG. 4. The teachingsof the present disclosure, however, also apply to other types ofcompressors utilizing other types of compression mechanisms.

For example, the compressor 10 may be a reciprocating compressor and thecompression mechanism may include at least one piston driven by a crankshaft for compressing refrigerant vapor. As another example, thecompressor 10 may be a rotary compressor and the compression mechanismmay include a vane mechanism for compressing refrigerant vapor. Further,while a specific type of heat pump system is shown in FIGS. 1A and 1B (arefrigeration system), the present teachings are also applicable toother types of heat pump systems, including other types of refrigerationsystems, HVAC systems, chiller systems, and other suitable types of heatpump systems where crankcase heating is used.

Refrigerant vapor from the compressor 10 is delivered to a condenser 12where the refrigerant vapor is liquefied at high pressure, therebyrejecting heat to the outside air. A condenser fan 13 may be implementedto regulate airflow past the condenser 12. The liquid refrigerantexiting the condenser 12 is delivered to an evaporator 16 through anexpansion valve 14. The expansion valve 14 may be a mechanical, thermal,or electronic valve for controlling super heat of the refrigerantentering the compressor 10.

The refrigerant passes through the expansion valve 14 where a pressuredrop causes the high pressure liquid refrigerant to achieve a lowerpressure combination of liquid and vapor. As hot air moves across theevaporator 16, the low pressure liquid turns into gas, thereby removingheat from the hot air adjacent the evaporator 16. While not shown, a fanis generally provided to facilitate airflow past the evaporator 16. Thelow pressure gas is delivered to the compressor 10 where it iscompressed to a high pressure gas, and delivered to the condenser 12 tostart the heat pump cycle again.

With reference to FIGS. 1A, 1B, 2 and 3, the compressor 10 may be drivenby a variable frequency drive (VFD) 22 that is housed in an enclosure20. Variable frequency drives are also referred to as inverters andinverter drives. The enclosure 20 may be located near or away from thecompressor 10.

For example, with reference to FIG. 1A, the VFD 22 is shown near thecompressor 10. For another example, as shown in FIGS. 2 and 3, the VFD22 may be attached (as part of the enclosure 20) to the compressor 10.For yet another example, with reference to FIG. 1B, the VFD 22 may belocated away from the compressor 10 by a separation 17. The separation17 may include, for example, a wall of a building. In other words, theVFD 22 may be located inside a building and the compressor 10 may belocated outside of the building or in a different room than thecompressor 10.

The VFD 22 receives an alternating current (AC) voltage from a powersupply 18 and delivers AC voltage to the compressor 10. The VFD 22 mayinclude a control module 25 with a processor and code operable tomodulate and control the frequency and/or amplitude of the AC voltagedelivered to an electric motor of the compressor 10.

The control module 25 may include a computer readable medium storingdata including the code executed by a processor to modulate and controlthe frequency and/or amplitude of voltage delivered to the compressor 10and to execute and perform the crankcase heating and control functionsdisclosed herein. By modulating the frequency and/or amplitude ofvoltage delivered to the electric motor of the compressor 10, thecontrol module 25 may modulate and control the speed, and consequentlythe capacity, of the compressor 10. The control module 25 also regulatesoperation of the condenser fan 13.

The VFD 22 may include solid state electronic circuitry to modulate thefrequency and/or amplitude of the AC voltage delivered to the compressor10. Generally, the VFD 22 converts the input AC voltage from AC to DC,and converts from DC back to AC at a desired frequency and/or amplitude.For example, the VFD 22 may directly rectify the AC voltage with afull-wave rectifier bridge. The VFD 22 may switch the voltage usinginsulated gate bipolar transistors (IGBTs) or thyristors to achieve thedesired output (e.g., frequency, amplitude, current, and/or voltage).Other suitable electronic components may be used to modulate thefrequency and/or amplitude of the AC voltage from the power supply 18.

Piping from the evaporator 16 to the compressor 10 may be routed throughthe enclosure 20 to cool the electronic components of the VFD 22 withinthe enclosure 20. The enclosure 20 may include a cold plate 15. Suctiongas refrigerant may cool the cold plate 15 prior to entering thecompressor 10 and thereby cool the electrical components of the VFD 22.In this way, the cold plate 15 may function as a heat exchanger betweensuction gas and the VFD 22 such that heat from the VFD 22 is transferredto suction gas prior to the suction gas entering the compressor 10.

However, as shown in FIG. 1B, the enclosure 20 may not include the coldplate 15 and thus the VFD 22 may not be cooled by suction gasrefrigerant. For example, the VFD 22 may be air cooled, such as with orwithout a fan. As a further example, the VFD 22 may be air cooled by thecondenser fan 13, provided the VFD 22 and the condenser 12 are locatedwithin sufficient proximity to each other. As shown in FIGS. 2 and 3,voltage from the VFD 22 may be delivered to the compressor 10 via aterminal box 24 attached to the compressor 10.

FIG. 4 includes an example cross-sectional view of the compressor 10.While a variable speed scroll compressor is shown and discussed, thepresent teachings of the present application are also applicable toother types of compressors, such as reciprocating compressors, androtary compressors.

The compressor 10 includes a stator 42 that magnetically turns a rotor44 to drive a crankshaft 46 in an on state. Power flow to the stator 42controls magnetization of the stator 42. Power can also be applied tothe stator 42 to control magnetization such that the rotor 44 is notdriven while power is applied to the stator 42, such as for crankcaseheating.

A lubricant sump 48 includes lubricant (e.g., oil) that lubricatesmoving parts of the compressor 10 such as the crankshaft 46. Thecompressor 10 also includes a fixed scroll and an orbiting scroll,generally indicated by 50. When the scrolls 50 are meshed, rotation ofthe crankshaft 46 drives one of the scrolls 50 to compress refrigerantthat is received through a suction tube 52. The scrolls 50 can beunmeshed under some circumstances such that the scrolls 50 do notcompress refrigerant.

An ambient temperature sensor 30 measures outdoor ambient temperature(OAT) outside of the compressor 10 and/or the enclosure 20. In variousimplementations, the ambient temperature sensor 30 may be included aspart of an existing system and thus be available via a sharedcommunication bus.

A compressor temperature sensor 32 measures a temperature (Compressortemperature) of the compressor 10. For example only, the compressortemperature sensor 32 may measure temperature at the discharge line ofthe compressor 10, which may be referred to as discharge linetemperature (DLT). Other examples of the temperature measured by thecompressor temperature sensor 32 include, but are not limited to,temperature in the lubricant sump 48, temperature of the stator 42, atemperature at a top portion of the shell of the compressor 10, atemperature at a bottom portion of the shell, a temperature at a pointbetween the top and bottom portions of the shell, and another suitablecompressor temperatures. The temperature of the stator 42 may bemeasured or derived, for example, based on resistance of the motorwindings.

The control module 25 also regulates a lubricant temperature in thelubricant sump 48 of the compressor 10. More specifically, the controlmodule 25 regulates compressor crankcase heating (CCH) to control thelubricant temperature. In the present application, the stator 42operates as a crankcase heater and heats the crankcase of the compressor10 and therefore the lubricant, as discussed further below.

Referring now to FIG. 5, a functional block diagram of an exampleimplementation of a compressor crankcase heating (CCH) control module100 is presented. The CCH control module 100 may include, be a part of,or be independent of the control module 25.

A power control module 104 controls whether crankcase heating is on oroff. The power control module 104 generally maintains crankcase heatingoff while the compressor 10 is on. The power control module 104 maycontrol whether crankcase heating is on or off based on the OAT, thecompressor temperature, both the OAT and the compressor temperature,current date and time data, and/or one or more other suitableparameters.

A data receiving module 106 may receive the OAT, the compressortemperature, and the current date and time data and output the OAT, thecompressor temperature, and the current date and time. The datareceiving module 106 may filter, digitize, buffer, and/or perform one ormore processing actions on the received data.

A difference module 108 may determine a temperature difference based onthe OAT and the compressor temperature. For example, the differencemodule 108 may set the temperature difference equal to the compressortemperature minus the OAT. While setting the temperature differenceequal to the compressor temperature minus the OAT is discussed, thetemperature difference may alternatively be set equal to the OAT minusthe compressor temperature or an absolute value of a difference betweenthe compressor temperature and the OAT.

A real-time clock module 112 may track and provide the current date andtime data. The current date and time data may indicate a current date(date, month, year) and a current time. While the real-time clock module112 is shown as being implemented within the CCH control module 100, thecurrent date and time data may be provided in another manner. Forexample, the current date and time data may be provided by a thermostator via a network connection (e.g., by a server, a mobile device, oranother suitable type of external device including a processor).

As stated above, the power control module 104 controls whether crankcaseheating is performed based on the OAT, the compressor temperature, boththe OAT and the compressor temperature, current date and time data,and/or one or more other suitable parameters. FIG. 6 is a flowchartdepicting an example method of controlling crankcase heating.

Referring now to FIG. 6, control may begin with 204 when the compressor10 is on and compressor crankcase heating is off. At 204, the powercontrol module 104 determines whether the compressor 10 has transitionedto the off state. If 204 is false, control may remain at 204. If 204 istrue, the power control module 104 may maintain compressor crankcaseheating off for a first predetermined period at 208. In this manner, thepower control module 104 may maintain compressor crankcase heating offfor the first predetermined period after the compressor 10 is turnedoff. The first predetermined period may be calibratable (i.e., is ableto be calibrated) and may be set based on experimental data takenregarding the migration rate of liquid into the compressor shell afterthe compressor 10 is turned off relative to the volume of the compressorshell. For example only, the first predetermined period may be betweenapproximately 30 minutes and approximately 3 hours or another suitableperiod. The power control module 104 may use (i.e., turn on) compressorcrankcase heating when the compressor 10 is off, such as after the firstpredetermined period has passed.

FIG. 7 is a flowchart depicting another example method of controllingcompressor crankcase heating. Referring now to FIG. 7, control may beginwith 304 where compressor crankcase heating is off and the compressor 10is off. At 304, the power control module 104 determines whether thetemperature difference is less than a first predetermined temperature.In other words, the power control module 104 may determine whether thecompressor temperature minus the OAT is less than the firstpredetermined temperature at 304. If 304 is false, the power controlmodule 104 may leave the on/off state of compressor crankcase heatingunchanged. If 304 is true, the power control module 104 may turncompressor crankcase heating on at 308. The first predeterminedtemperature may be calibratable and may be set based on experimentaldata taken regarding temperatures where cold start and/or liquidflood-back occurs. For example only, the first predetermined temperaturemay be approximately 0 (zero) degrees Fahrenheit or another suitabletemperature below which cold start and/or liquid flood-back may occur.

The power control module 104 may maintain compressor crankcase heatingon, for example, for a second predetermined period and/or, as discussedfurther below, until the temperature difference becomes greater than asecond predetermined temperature. The second predetermined period may becalibratable and may be set, for example, based on experimental datataken regarding a period of compressor crankcase heating necessary toincrease the temperature difference to greater than the secondpredetermined temperature. The second predetermined period may be afixed value or a variable value. In the case of the second predeterminedperiod being a variable value, the power control module 104 maydetermine the second predetermined period, for example, as a function ofthe compressor temperature and/or the OAT. In the case of the secondpredetermined temperature being a fixed value, the second predeterminedtemperature may be, for example, approximately 10 degrees Fahrenheit,approximately 15 degrees Fahrenheit, approximately 20 degreesFahrenheit, or another suitable temperature that is greater than thefirst predetermined temperature.

FIG. 8 is a flowchart depicting another example method of controllingcompressor crankcase heating. Referring now to FIG. 8, control may beginwith 404 where compressor crankcase heating is on and the compressor 10is off. At 404, the power control module 104 determines whether thetemperature difference is greater than the second predeterminedtemperature. In other words, the power control module 104 may determinewhether the compressor temperature minus the OAT is greater than thesecond predetermined temperature at 404. If 404 is false, the powercontrol module 104 may maintain the on/off state of compressor crankcaseheating unchanged. If 404 is true, the power control module 104 may turncompressor crankcase heating off at 408. As stated above, the secondpredetermined temperature may be calibratable and may be set to, forexample, approximately 10 degrees Fahrenheit, approximately 15 degreesFahrenheit, approximately 20 degrees Fahrenheit, or another suitabletemperature that is greater than the first predetermined temperature.

FIG. 9 is a flowchart depicting another example method of controllingcompressor crankcase heating. Referring now to FIG. 9, control may beginwith 504 where the compressor 10 is off. At 504, the power controlmodule 104 determines whether the OAT is greater than a thirdpredetermined temperature. If 504 is false, the power control module 104may maintain the on/off state of compressor crankcase heating unchanged.If 504 is true, the power control module 104 may turn compressorcrankcase heating off at 508. The third predetermined temperature may becalibratable and may be set, for example, based on experimental datataken regarding temperatures where compressor crankcase heating is notneeded (e.g., where cold start and liquid-flood back are not a concern).For example only, the third predetermined temperature may be set toapproximately 75 degrees Fahrenheit or another suitable temperature.

FIG. 10 is a flowchart depicting another example method of controllingcompressor crankcase heating. Referring now to FIG. 10, control maybegin with 604 where the power control module 104 determines whether aperiod that the compressor 10 has been off is greater than a thirdpredetermined period. The period that the compressor 10 has been off(continuously) since the compressor 10 was last turned off can bereferred to as a compressor off period. A timer module 116 (see FIG. 5)may reset and start the compressor off period in response to receipt ofan indicator that the compressor 10 has been turned off.

If the compressor off period is greater than the third predeterminedperiod, control may continue with 608. If the compressor off period isnot greater than the second predetermined period, the power controlmodule 104 may leave the on/off state of compressor crankcase heatingunchanged. The third predetermined period may be calibratable and may beset, for example, to approximately 3 weeks or another suitable period.

At 608, the power control module 104 may determine whether the OAT andthe compressor temperature are both less than a fourth predeterminedtemperature. If 608 is true, the power control module 104 may turn theCCH off at 612. If 608 is false, the power control module 104 maymaintain the on/off state of compressor crankcase heating unchanged. Thefourth predetermined temperature may be calibratable and may be set, forexample, to approximately 55 degrees Fahrenheit or another suitabletemperature that is less than the third predetermined temperature.

The compressor off period being greater than the second predeterminedperiod may indicate that the heat pump system (and more specifically airconditioning) has been shut down for the season (e.g., seasonally forwinter). The compressor temperature and/or the OAT being less than thefourth predetermined temperature may be used to verify that thecompressor 10 has been shut down. In various implementations, 608 may beomitted, and the power control module 104 may turn compressor crankcaseheating off in response to a determination that the compressor offperiod is greater than the second predetermined period.

FIG. 11 is a flowchart depicting another example method of controllingcompressor crankcase heating. Referring now to FIG. 11, control maybegin with 704 where the compressor 10 is off. At 704, the power controlmodule 104 determines whether the current date indicated in the currentdate and time data is within a predetermined date range. If 704 isfalse, control may leave the on/off state of compressor crankcaseheating unchanged. If 704 is true, the power control module 104 may turncompressor crankcase heating off at 708. The predetermined date rangemay be calibratable and may be set, for example, to approximatelyNovember 1 through approximately April 1, yearly, or another suitabledate range when the heat pump system (and more specifically airconditioning) is expected to remain off.

FIG. 12 is a flowchart depicting another example method of controllingcompressor crankcase heating. Referring now to FIG. 12, control maybegin with 804 where the compressor 10 is off. At 804, the power controlmodule 104 determines whether the current time indicated in the currentdate and time data is within a predetermined time range. If 804 isfalse, the power control module 104 may leave the on/off state ofcompressor crankcase heating unchanged. If 804 is true, the powercontrol module 104 may turn compressor crankcase heating off at 808. Thepredetermined time range may be calibratable and may be set, forexample, to approximately 12:00 am to approximately 10:00 am, daily, oranother suitable daily time range when the heat pump system (and morespecifically air conditioning) is expected to remain off.

FIG. 13 is a flowchart depicting another example method of controllingcompressor crankcase heating. Referring now to FIG. 13, control maybegin with 904 where the compressor 10 is off. At 904, the power controlmodule 104 determines whether the current date and time is within apredetermined system OFF period. The predetermined system OFF period mayrefer to a period from entry into the predetermined system OFF periodwhen the heat pump system will remain off. The predetermined system OFFperiod may be provided by a user via the thermostat or via a networkconnection (e.g., by a server or a mobile device).

The power control module 104 may record the current date and time whenthe predetermined system OFF period is provided. If the current date andtime is within the predetermined system OFF period following therecorded date and time, the power control module 104 may turn compressorcrankcase heating off at 908. If the current date and time is outside ofthe predetermined system OFF period following the recorded date andtime, the power control module 104 may leave the on/off state ofcompressor crankcase heating unchanged.

FIG. 14 is a flowchart depicting another example method of controllingcompressor crankcase heating. Referring now to FIG. 14, control maybegin with 1004 where the compressor 10 is off. Compressor crankcaseheating may also be off at 1004. At 1004, the power control module 104determines whether the compressor off period is greater than the thirdpredetermined period and the OAT and the compressor temperature are lessthan the fourth predetermined temperature. If 1004 is true, the powercontrol module 104 may turn compressor crankcase heating off at 1036. If1004 is false, control may continue with 1008.

At 1008, the power control module 104 determines whether the currentdate indicated by the current date and time data is within thepredetermined date range. If 1008 is true, the power control module 104may turn compressor crankcase heating off at 1036. If 1008 is false,control may continue with 1012. The power control module 104 determineswhether the current date and time is within the predetermined system OFFperiod at 1012. If 1012 is true, the power control module 104 may turncompressor crankcase heating off at 1036. If 1012 is false, control maycontinue with 1016.

The power control module 104 determines whether the current timeindicated by the current date and time data is within the predeterminedtime range at 1016. If 1016 is true, the power control module 104 mayturn compressor crankcase heating off at 1036. If 1016 is false, controlmay continue with 1020. At 1020, the power control module 104 determineswhether the OAT is greater than the third predetermined temperature. If1020 is true, the power control module 104 may turn compressor crankcaseheating off at 1036. If 1020 is false, control may continue with 1024.

At 1024, the power control module 104 determines whether the temperaturedifference is less than the first predetermined temperature. If 1024 istrue, the power control module 104 may turn compressor crankcase heatingon at 1028, and control may continue with 1032. If 1024 is false,control may end.

At 1032, the power control module 104 determines whether the temperaturedifference is greater than the second predetermined temperature. If 1032is true, the power control module 104 may turn compressor crankcaseheating off at 1036. If false, the power control module 104 may leavecompressor crankcase heating on and remain at 1032. While the aboveorder has been provided for 1004-1036, the order of execution of one ormore of 1004-1036 may be changed.

FIGS. 15A, 15B, and 15C are functional block diagrams of examplecompressor crankcase heating systems of example single phase heat pumpsystems. Specifically, a stator 1104 of an electric motor of thecompressor 10 acts as a crankcase heater. The stator 1104 includes a runwinding 1108 that is connected between a run node (R) and a common node(C). The stator 1104 also includes a start winding 1112 that isconnected between a start node (S) and the common node (C).

In the example of FIG. 15A, compressor crankcase heating is performedusing the start winding 1112. In the example of FIG. 15B, compressorcrankcase heating is performed using the run winding 1108. In theexample of FIG. 15C, compressor crankcase heating is performed usingboth the start winding 1112 and the run winding 1108.

Referring now to FIG. 15A, first and second power lines (L1 and L2) areconnected to first and second inputs of a contactor 1116. While thecontactor 1116 is shown and discussed, one or more other suitable typesof switching devices may be used. The first and second power linesreceive a first voltage, such as approximately 220 Volts alternatingcurrent (VAC) or another voltage suitable for operation of thecompressor 10. For example, the first and second power lines may receivepower output by the VFD 22. While the present application will bediscussed in terms of the first voltage being an AC voltage, the firstvoltage may instead be a direct current (DC) voltage.

First and second outputs of the contactor 1116 are connected to firstand second nodes 1120 and 1124. The contactor 1116 selectively connectsand disconnects its first input to/from its first output and its secondinput to/from its second output, as discussed further below. Theelectric motor of the condenser fan 13 may be connected to the first andsecond nodes 1120 and 1124.

The first node 1120 is connected to the run node (R). A capacitor 1128is connected between the first node 1120 and a first input of a firstswitching device 1132. A second input of the first switching device 1132is connected to a third power line (P3), and an output of the firstswitching device 1132 is connected to the start node (S). The firstswitching device 1132 connects either its first input or its secondinput to its output at a given time.

The second node 1124 is connected to a first input of a second switchingdevice 1136. A second input of the second switching device 1136 isconnected to a fourth power line (P4). An output of the second switchingdevice 1136 is connected to the common node (C). The first switchingdevice 1132 connects either its first input or its second input to itsoutput at a given time.

The third and fourth power lines (P3 and P4) receive a second voltagethat is less than the first voltage received by the first and secondpower lines (L1 and L2). The second voltage is used to performcompressor crankcase heating while the compressor 10 is off. For exampleonly, the second voltage may be approximately 24 VAC or another suitablevoltage that is less than the first voltage. The second voltage may alsobe used to power the CCH control module 100.

Using second voltage for compressor crankcase heating is more efficientthan using the first voltage. Additionally, as the motor of thecondenser fan 13 may also be connected to the first and second nodes1120 and 1124, compressor crankcase heating may be performed without thecondenser fan 13 being turned on. This further increases efficiency.While use of an AC voltage for the second voltage is discussed, invarious implementations, such as in the examples of FIGS. 16 and 17A-C,a direct current (DC) voltage that is less than (e.g., a peak value of)the first voltage may be used.

The second voltage may be supplied by an indoor unit 1140 or anothersuitable power supply. For example, the indoor unit 1140 receivesalternating current (AC) power, such as a 110 VAC input, from a utility.The indoor unit 1140 includes various components, such as the expansionvalve 14, the evaporator 16, and a blower or fan.

The indoor unit 1140 also includes a transformer 1144. The transformer1144 outputs the second voltage based on the power input to thetransformer 1144. For example, the transformer 1144 may generate 24 VACbased on a 110 VAC input. The indoor unit 1140 outputs the secondvoltage to a thermostat 1148.

The thermostat 1148 controls the contactor 1116. For example, the thirdpower line may be connected to a first end of a controlling element 1152of the contactor 1116. A second end of the controlling element 1152 ofthe contactor 1116 may be connected to the fourth power line via aswitching element 1156 of the thermostat 1148.

Opening/closing of the switching device 1156 controls current flowthrough the controlling element 1152 of the contactor 1116. Current flowthrough the controlling element 1152 (when the switching device 1156 isclosed) causes the first input of the contactor 1116 to be connected tofirst output of the contactor and causes the second input of thecontactor 1116 to be connected with the second output of the contactor1116. Lack of current flow through the controlling element 1152 (e.g.,when the switching device 1156 is open) causes the first input of thecontactor 1116 to be disconnected from first output of the contactor1116 and causes the second input of the contactor 1116 to bedisconnected from the second output of the contactor 1116.

The thermostat 1148 opens and closes the switching device 1156 based ona temperature of air within a space. For example, the thermostat 1148may close the switching device 1156 when the temperature of air withinthe space is greater than a target temperature for the air within thespace to cool the space. The thermostat 1148 may open the switchingdevice 1156, for example, when the temperature of the air within thespace is less than the target temperature by at least a predeterminedamount. The thermostat 1148 closes the switching device 1156 to turn thecompressor 10 on. The thermostat 1148 opens the switching device 1156 toturn the compressor 10 off.

A high-pressure cutoff (HPCO) device 1160 and a low-pressure cutoff(LPCO) device 1164 may be connected between the second end of thecontrolling element 1152 and the switching device 1156. The HPCO device1160 may disable current flow through the controlling element 1152 ofthe contactor 1116 (to disconnect the first and second inputs from thefirst and second outputs of the contactor 1116, respectively) when anoutput pressure of the compressor 10 is greater than a firstpredetermined pressure. The output pressure of the compressor 10 mayalso be referred to as a discharge pressure.

The LPCO device 1164 may disable current flow through the controllingelement 1152 of the contactor 1116 (to disconnect the first and secondinputs from the first and second outputs of the contactor 1116,respectively) when an input pressure of the compressor 10 is less than asecond predetermined pressure. The input pressure of the compressor 10may also be referred to as a suction pressure. While the HPCO device1160 and the LPCO device 1164 are shown and discussed, one or both ofthe HPCO device 1160 and the LPCO device 1164 may be omitted in variousimplementations.

As noted above, compressor crankcase heating is performed using the runwinding 1108 in the example of FIG. 15B. Referring now to FIG. 15B, thefirst input of the first switching device 1132 may be connected to thefirst node 1120, and the third power line (P3) may be connected to thesecond input of the first switching device 1132. The output of the firstswitching device 1132 may be connected to the run node (R). With thisconfiguration, the second voltage can be applied only to the run winding1108 for compressor crankcase heating. In FIG. 15A, the second voltagecan be applied only to the start winding 1112 for compressor crankcaseheating.

Compressor crankcase heating is performed using both the start winding1112 and the run winding 1108 in the example of FIG. 15C. Referring nowto FIG. 15C, the first input of the first switching device 1132 isconnected to the first node 1120, the second input of the firstswitching device 1132 is connected to the third power line (P3), and theoutput of the first switching device 1132 is connected to the run node(R). The capacitor 1128 is connected between the output of the firstswitching device 1132 and the start note (S). Thus, in FIG. 15C, powercan be applied to both the run winding 1108 and the start winding 1112for compressor crankcase heating.

As noted above, a DC voltage can be applied to the second inputs of thefirst and second switching devices 1132 and 1136. In other words, thesecond voltage can be a DC voltage.

FIG. 16 includes another functional block diagram of the exampleimplementation of the CCH control module 100. Referring now to FIG. 16,the CCH control module 100 may be connected to receive the AC voltageoutput by the transformer 1144. For example, the CCH control module 100may receive the AC voltage from the thermostat 1148. In variousimplementations, the timer module 116 may use the input from thethermostat 1148 to determine whether the compressor 10 is on or off.

The CCH control module 100 may include a rectifier 1204 that convertsthe received AC voltage into a DC voltage. The CCH control module 100may also include a capacitor 1208 that smoothes the DC voltage. Whileonly the capacitor 1208 is shown and discussed, more than one capacitormay be used.

In various implementations, the CCH control module 100 may include oneor more other components (e.g., an inductor and a switching device) toboost the DC voltage to greater than the peak of the received ACvoltage. For example, the CCH control module 100 may boost the DCvoltage to approximately 40 Volts DC or another suitable voltage that isless than the first voltage. The CCH control module 100 outputs the DCvoltage via first and second DC lines (VDCp and VDCn).

FIGS. 17A, 17B, and 17C include example compressor crankcase heatingcontrol systems similar to those of FIGS. 15A, 15B, and 15C,respectively. In FIGS. 17A, 17B, and 17C, the first DC line (VDCp) isconnected to the second input of the first switching device 1132, andthe second DC line (VDCn) is connected to the second input of the secondswitching device 1136. In this manner, the DC voltage output by the CCHcontrol module 100 is applied to the first and second switching devices1132 and 1136 for compressor crankcase heating.

Referring now to FIGS. 15A-C and FIGS. 17A-C, the CCH control module 100controls the first and second switching devices 1132 and 1136 to controlcompressor crankcase heating. As discussed above, compressor crankcaseheating is performed when the compressor 10 is off (i.e., when thecontactor 1116 is open), for example, as described in conjunction withthe examples of FIGS. 6-14.

When the contactor 1116 is closed (so the motor of the compressor 10 candrive the crankshaft), the CCH control module 100 controls the firstswitching device 1132 such that its first input is connected to itsoutput and controls the second switching device 1136 such that its firstinput is connected to its output. Power from the first and second powerlines (L1 and L2) flows through the first and second switching devices1132 and 1136 and drives the compressor 10.

The thermostat 1148 opens the contactor 1116 to turn the compressor 10off. When the compressor 10 is turned off, the CCH control module 100may maintain the first switching device 1132 such that its first inputis connected to its output and the second switching device 1136 suchthat its first input is connected to its output. As the first and secondpower lines are disconnected from the first and second nodes 1120 and1124 when the contactor 1116 is open, the compressor 10 is off and nocompressor crankcase heating is performed because no power is applied tothe run winding 1108 and/or the start winding 1112.

When the contactor 1116 is open (and the compressor 10 is thereforeoff), the CCH control module 100 performs compressor crankcase heatingby controlling the first switching device 1132 such that its secondinput is connected to its output and controls the second switchingdevice 1136 such that its second input is connected to its output. Thesecond voltage (AC or DC) then flows through the start winding 1112(e.g., as in FIGS. 15A and 17A), the run winding 1108 (e.g., as in FIGS.15B and 17B), or both the start winding 1112 and the run winding 1108(e.g., as in FIGS. 15C and 17C).

The first and second switching devices 1132 and 1136 may be any suitabletype of switching devices that remains operable when the contactor 1116is closed and the compressor 10 is on. In this manner, the first andsecond switching devices 1132 and 1136 will also remain operable whenthe contactor 1116 is open and crank case heating is being performed.

For example, when the second voltage is an AC voltage, the first andsecond switching devices 1132 and 1136 may include relays, triacs,silicon control rectifiers (SCRs), or another suitable type of switchingdevice. If the second voltage is a DC voltage, the first and secondswitching devices 1132 and 1136 may include metal oxide semiconductorfield effect transistors (MOSFETs), insulated gate bipolar transistors(IGBTs), or another suitable type of switching device.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.” Itshould be understood that one or more steps within a method may beexecuted in different order (or concurrently) without altering theprinciples of the present disclosure.

In this application, including the definitions below, the term ‘module’or the term ‘controller’ may be replaced with the term ‘circuit.’ Theterm ‘module’ may refer to, be part of, or include: an ApplicationSpecific Integrated Circuit (ASIC); a digital, analog, or mixedanalog/digital discrete circuit; a digital, analog, or mixedanalog/digital integrated circuit; a combinational logic circuit; afield programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks andflowchart elements described above serve as software specifications,which can be translated into the computer programs by the routine workof a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory, tangible computer-readablemedium. The computer programs may also include or rely on stored data.The computer programs may encompass a basic input/output system (BIOS)that interacts with hardware of the special purpose computer, devicedrivers that interact with particular devices of the special purposecomputer, one or more operating systems, user applications, backgroundservices, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language) or XML (extensible markuplanguage), (ii) assembly code, (iii) object code generated from sourcecode by a compiler, (iv) source code for execution by an interpreter,(v) source code for compilation and execution by a just-in-timecompiler, etc. As examples only, source code may be written using syntaxfrom languages including C, C++, C#, Objective C, Haskell, Go, SQL, R,Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5,Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang,Ruby, Flash®, Visual Basic®, Lua, and Python®.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. §112(f)unless an element is expressly recited using the phrase “means for,” orin the case of a method claim using the phrases “operation for” or “stepfor.”

What is claimed is:
 1. A compressor crankcase heating control system fora heat pump system, the compressor crankcase heating control systemcomprising: a first switching device that includes a first inputconnected to a first power line, that includes a second input connectedto a second power line, the first and second power lines for receiving afirst voltage, and that selectively connects and disconnects the firstand second inputs to and from first and second nodes, respectively; asecond switching device that includes a third input that is connected tothe first node, that includes a fourth input that is connected to athird power line, and that includes a first output that is connected toa first end of a stator winding of an electric motor of a compressor; athird switching device that includes a fifth input that is connected tothe second node, that includes a sixth input that is connected to afourth power line, the third and fourth power lines for receiving asecond voltage that is less than the first voltage, and that includes asecond output that is connected to a second end of the stator winding ofthe electric motor of the compressor; and a compressor crankcase heatingcontrol module that controls the second and third switching devices. 2.The compressor crankcase heating control system of claim 1 wherein, whenthe first and second inputs are disconnected from the first and secondnodes, respectively, the compressor crankcase heating control moduleselectively: actuates the second switching device to connect the fourthinput to the first output; and actuates the third switching device toconnect the sixth input to the second output.
 3. The compressorcrankcase heating control system of claim 2 wherein, when the first andsecond inputs are disconnected from the first and second nodes,respectively, the compressor crankcase heating control moduleselectively actuates the second and third switching devices based on atleast one of a temperature of the compressor, an ambient temperature, acurrent date, and a current time.
 4. The compressor crankcase heatingcontrol system of claim 2 wherein, when the first and second inputs areconnected to the first and second nodes, respectively, the compressorcrankcase heating control module: actuates the second switching deviceto connect the third input to the first output; and actuates the thirdswitching device to connect the fifth input to the second output.
 5. Thecompressor crankcase heating control system of claim 1 furthercomprising a thermostat that actuates the first switching device basedon a temperature within a space and a predetermined temperature.
 6. Thecompressor crankcase heating control system of claim 5 furthercomprising an indoor unit that includes an evaporator, a blower, and atransformer, the transformer generating the second voltage based on athird voltage and outputting the second voltage to the thermostat. 7.The compressor crankcase heating control system of claim 6 wherein thirdvoltage is: less than the first voltage; and greater than the secondvoltage.
 8. The compressor crankcase heating control system of claim 5wherein the second voltage is approximately 24 Volts.
 9. The compressorcrankcase heating control system of claim 1 further comprising: anindoor unit that includes an evaporator, a blower, and a transformer,the transformer generating a third voltage based on a fourth voltage andoutputting the third voltage; and a thermostat that outputs the thirdvoltage to the compressor crankcase heating control module, wherein thecompressor crankcase heating control module generates the second voltagebased on the third voltage and outputs the second voltage.
 10. Thecompressor crankcase heating control system of claim 9 wherein: thethird voltage is less than the fourth voltage; and the second voltage isgreater than the third voltage.
 11. The compressor crankcase heatingcontrol system of claim 1 wherein the stator winding is a start winding.12. The compressor crankcase heating control system of claim 1 whereinthe stator winding is a run winding.
 13. The compressor crankcaseheating control system of claim 1 further comprising an electric motorof a condenser fan that is connected to the first and second nodes. 14.A compressor crankcase heating control system for a heat pump system,the compressor crankcase heating control system comprising: a firstswitching device that includes a first input connected to a first powerline, that includes a second input connected to a second power line, thefirst and second power lines for receiving a first voltage, and thatselectively connects and disconnects the first and second inputs to andfrom first and second nodes, respectively; a second switching devicethat includes a third input that is connected to the first node, thatincludes a fourth input that is connected to a third power line, andthat includes a first output that is connected to: a first end of afirst winding of a stator of an electric motor of a compressor; and afirst end of a second winding of the stator of the electric motor of thecompressor; a third switching device that includes a fifth input that isconnected to the second node, that includes a sixth input that isconnected to a fourth power line, the third and fourth power lines forreceiving a second voltage that is less than the first voltage, and thatincludes a second output that is connected to second ends of the firstand second windings of the stator of the electric motor of thecompressor; and a compressor crankcase heating control module thatcontrols the second and third switching devices.
 15. The compressorcrankcase heating control system of claim 14 wherein, when the first andsecond inputs are disconnected from the first and second nodes,respectively, the compressor crankcase heating control moduleselectively: actuates the second switching device to connect the fourthinput to the first output; and actuates the third switching device toconnect the sixth input to the second output.
 16. The compressorcrankcase heating control system of claim 15 wherein, when the first andsecond inputs are disconnected from the first and second nodes,respectively, the compressor crankcase heating control moduleselectively actuates the second and third switching devices based on atleast one of a temperature of the compressor, an ambient temperature, acurrent date, and a current time.
 17. The compressor crankcase heatingcontrol system of claim 15 wherein, when the first and second inputs areconnected to the first and second nodes, respectively, the compressorcrankcase heating control module: actuates the second switching deviceto connect the third input to the first output; and actuates the thirdswitching device to connect the fifth input to the second output.
 18. Aheat pump system comprising: first and second heat exchangers; anexpansion valve; a compressor that includes an electric motor includinga stator, the stator including a first winding and a second winding; afirst switching device that includes a first input connected to a firstpower line, that includes a second input connected to a second powerline, the first and second power lines for receiving a first voltage,and that selectively connects and disconnects the first and secondinputs to and from first and second nodes, respectively; a secondswitching device that includes a third input that is connected to thefirst node, that includes a fourth input that is connected to a thirdpower line, and that includes a first output that is connected to atleast one of a first end of the first winding and a first end of thesecond winding; a third switching device that includes a fifth inputthat is connected to the second node, that includes a sixth input thatis connected to a fourth power line, the third and fourth power linesfor receiving a second voltage that is less than the first voltage, andthat includes a second output that is connected to a second end of thefirst winding and a second end of the second winding; and a compressorcrankcase heating control module that includes a processor and memory,the memory including instructions executed by the processor for: whenthe first and second inputs are disconnected from the first and secondnodes, respectively: actuating the second switching device to connectthe fourth input to the first output; and actuating the third switchingdevice to connect the sixth input to the second output; and, when thefirst and second inputs are connected to the first and second nodes,respectively: actuating the second switching device to connect the thirdinput to the first output; and actuating the third switching device toconnect the fifth input to the second output.
 19. The heat pump systemof claim 18 further comprising an indoor unit that includes atransformer and one of the first and second heat exchangers, wherein thetransformer generates the second voltage based on a third voltage. 20.The heat pump system of claim 18 further comprising an indoor unit thatincludes a transformer and one of the first and second heat exchangers,wherein the transformer generates a third voltage based on a fourthvoltage and outputs the third voltage to a thermostat, and wherein thecompressor crankcase heating control module generates the second voltagebased on the third voltage.